Radio telephone and telegraph system



Sept. 22, 1931. T, A. MCCANN RADIO TELEPHONE AND TELEGRAPH SYSTEM Filed July 19. 1929 2 Sheets-Sheet l AI @Si lNvENToR Z'cuuz/ ATTORN EY Sept. 22, 1931. T. A. MccANN RADIO TELEPHONE AND TELEGRAP SYSTEM Filed July 19. 1929 2 Sheets-Sheet 2 QN 17 r ATTORNEY Patented Sept. Z2, 1931 siren STATI-:vs vPA'rlaN'i- Vori-lcs THOMAS A. MCGANN, OF ORANGE, NEW JERSEY, ASSIGNOR TOv 'TELEPHONE .AND TELES-BAPE COMPANY, A CORPORATION lO1? NEW YORK nAnro TELEPHONEAND TELEGRAPH SYSTEM Application filed July 19, 1929. Serial No. 379,491.

`Where a radio link is used for establishing telephone connections between two distant points, such, for example, as New York and London, it 1s desirable to utilize theradic apparatus which is normally employedfor telephone transmission, for the transmission of telegraph messages. when the apparatus is not employed for telephone'purposes. it is particularly desirable tocuse the radio telephone apparatus for the transmission of telegraphic messages between operators in connection with theestablishment of telephone connections. Arrangements have been provided, therefore, for enabling such use of the radio telephone chan nel for telegraph purposes during idle periods.

In such arrangements of the prior art, certain diiiiculties have been encountered when the telegraph part of the system is operated on a full duplex basis. rIn'full duplex operation the system is so set up that telegraph messages may be sent simultaneously in both directions. `With the system as heretofore operated, the telegraph signals were transmitted as an 'interrupted tone. YWhile tones of different frequencies were employed for sending and receiving, the tone used for sending was sometimesreceived by the local radio Vreceiver. as interference of such magnitude as to overload the repeaters in the receiving line extending from the radio receiver to the local telegraph receiving apparatus. This resulted in mutilation and sometimes loss of signals, and it was therefore necessary to pr vide a relay train responsive to the sending tone for automatically cutting a suppression ilter in at the radio receiver `to prevent the sending tone from being transmitted through the repeaters of the receiving line. Y

Since it was undesirable that this relay train operate in response to static or un Voperate in response to the sending tone unless the tone had been applied continuously for an interval longer than any corresponding tone frequency would persist in the case of telephone or static signals. As the relay train onlyoperates to cut in the filter when the local telegraph transmitter is applied to thecircuit, received signals would be lost if the distant telegraph operator should `applyV her sending telegraph apparatus to the radio channel'V and start sending before the local operator applies her telegraph transmitterto the circuit. This arises from the fact that a tone from the local transmitter would be received as interference at the local radio receiver and thereby cause mutilation of received signals until the relay train has had time to operate and cut in the suppression filter.

' ln order to obviate this difficulty it is proposed in accordance with the present inoperate automatic switching means forY switching the tone from the local telegraph senderrto theradiotransmitting channel, thereby causing the relay train associated With the local receiver to operate and cut in the suppression filter. The local operator may then plug up the telegraph sender to the radio circuit in the usual manner independently of the automatic tone connection previously established whenever it is desired to send messages in the yopposite direction. This plugging up operation, with the ensuing transmission of telegraph signals, will not cause any` intereference with received signals because the suppression filter will have already been connected in circuit at the local radio receiver. Preferably the circuit is so arranged that when the local operator takes' down the connection vto the telegraph sender the tone will be removed from the circuit.

The invention will now be more fully understood from the following detailed description thereof whenV read in connection With the accompanying drawings, Figure/1 lsii of which illustrates a circuit arrangement embodying the principles of the invention applied to a radio telephone system, and F ig. 2 of which illustrates the invention applied to a wire transmission system. In the drawings, the circuit arrangement and apparatus at one terminal only of the radio link is shown, it being understood that the apparatus at the other terminal will be similar to that illustrated.

lReferring to the drawings, a radio trans- -mitter is conventionally,indicated at T, and

similarly a radio receiver is conventionally indicated at R. The receiver and transmitter are located some distance apart in order to reduce interference in the receiver from the local transmitter. The radio receiver and radio transmitter are connected by means of a four-wire circuit to a telephone oflice at which switching connections are established to any desired telephone circuit by means of a cord C, which may-connect the terminal Vjack J of the four-wire Vcircuitwith'a jack J of a desired telephone line by means of the plugs P and P. The four-wire circuit comprises Yone-way lines TL and RL connected together at the telephone oili'ce through a hybrid coil 10 and balancing network N, `in a well-known manner. The lines-TL and RL are Vone-way lines, the line TL-being arranged to transmit from the terminal jack J to' the radio transmitter T and the line RL being arranged to transmit from the radio-receiver R to the -jack J. Either or both of these lines may include a number of repeaters (not shown) for amplifying the telephone currents transmitted' thereover.

In order to prevent singing over the overall four-wire circuit including the radio paths tol the distant terminal, and also to prevent singing over the local circuit from the transmitter T to the receiver R, over the line RL, through the hybrid coil 10, and over the line TL to the radio transmitter, the line TL is normally disabled. Voice-operated devices are provided whereby when transmission takes place from the jack J over the line TL to the transmitter T, the line TL is put in operative condition and the line RL is disabled. When, however, transmission takes place from the receiver'R over the line RL to the jack J the line TL is maintained disabled. This is accomplished by associating with each oneway line a voice-operated device for controlling a short-circuit across the other line. In the case of the line TL this apparatus comprises an amplifier-detector unit of wellknown type TV associated with the line TL, said unit controlling relays TVR and TVR. When voice currents enter the amplifierdetector TV the relays TVR and TVR are l energized, the latter opening the normal short-'circuit across the line TL and permitting transmission to take place from jack J y to the transmitter T, and the former closing a short-circuit across the line RL and the input termina-ls of an amplifier-detector unit RV.associated with the line RL.

The amplifier-detector unit RV is associatedA with the line RL and responds to voice currents received from the radio receiver R and transmitted over the line RL to energize a relay RVR in a well-known manner, so that thelatter short-circuits the line vTL independently of the normal shortcircuitA controlled by the relay TVR. The short-circuit thus applied to the line TL also serves to short-circuit the amplifier detector-TV to prevent false operation. Delay networksv TDN and` RDN arel associated with the lines TL and RL, respectively, to enable the voice-controlled switching devices to perform their oiiices before the voice currents arrive at the points in the circuits which are affected by the switching operations. For example, when voice currents are transmitted from the jack J over yvoice currents have an opportunity to pass through the hybrid coil l0 (dueto unbalance) andrenter the line TL. i

During periods'when the circuit above described is not being used for telephone operation, it is desirable to use the radio facilities for the transmission of telegraph messages, and more particularly it is desirable to transmit printer messages between operators to give directions necessary to the establishment of telephone connections over the radio link. In order to transmit such telegraph messages from the telephone otlice shown to a distant .telephone ofiice associated with the distant terminall of the radio link, the cord C, which is used for setting up telephone connections, may have its plug P inserted in a jack J which is connected to a telegraph transmitter. This transmitter may comprise a transmitting printer unit conventionally indicated at TP which, by means of marking and spacing signals, controls arelay TR. The contact of this relay is arranged to open and close a short-circuit across the terminals of a tone source G connected to the tip and ring conductor of the ack J. For reasons that will more fully appear hereinafter the relay TR has its contact so arranged as to open the short-circuit across the tone source G during marking impulses and to close the shortcircuit during spacing impulses.A Consequently, an audible tone will be applied to the terminals of the jack J and transmitted over the line TL to the radio transmitter during the marking intervals, while spacing signals will be represented by a no-tone condition of the circuit. The tone employed is preferably an audible frequency so that it may be transmitted over the circuit TL in the manner as voice currents are transmitted. A

Since, as has already been described, the line TL is normally disabled by means of the short-circuit applied by the relay TVR', it is necessary to render the connection over the line 'TL operative in order that .the printer signals may be transmitted. This f ilt is accomplished by a ground connecn established over the sleeve conductors the jack J, slug P, sleeve conductor of the cord C, sleeve conductors of the plug P, and the telegraph jack J and thence over a conductor 20, through the windings of relays TVR and TVR to the plate battery. This causes the energization of relays TVR and TVR independently of the plate circuit of the amplifier-detector unit TV and maintains these relays operated as long as the telegraph connection is established. The short-circuit c is, therefore, removed from the line TL so that the tone correspondingto the marking signals may be transmitted over the line TL to the radio transmitter T, where it is modulated upon the radio carrier in the same way as ordinary telephone currents, and transmitted to the radio receiver at the distant radio terminal` The energization of the relay TVR, however, short-circuits the line RL between the amplifier rRA and the delay network RDN so that transmission cannot take place from the radio receiver R over the line RL to the jack J. t is, therefore, necessary that the telegraph receivingV apparatus be associated with the line RL for reception of telegraph signals from the distant station in such manner as not to be affected by the short-circuit controlled by the relay TVR. Accordingly, -such telegraph receiving apparatus is bridged across the line RL at zr-g/ between the point at which the short-circuit is applied and the radio receiver R. The one-way amplifier RA is then connected between the terminals c-g/ of the telegraph receiving apparatus and the point at which the short-circuit is applied by the relay TVR, so that the shortcircuit does not have any effect upon the telegraph receiving apparatus and transmission may take place from the radio receiver R over the line RL to the terminals w-y and thence into the telegraph receiving apparatus.

The telegraph signals received from the distant radio transmitter are applied to such radio transmitter as an interrupted tone in a manner similar t`o tl at already described to interference from the local transmitter T,`such telegraph receiving4 apparatus includes a filter RF for selecting the desired tone. An amplifier RA may also be proyided for amplifying the received current, and a detector RD of well-known type is provided for rectifying the tone to produce direct current signals corresponding to the telegraph impulses. he direct current impulses actuate the polar relay PRH, as will be described in more detail later, and by means of this relay are transmitted to the receiving printer conventionally indicated at RP, as will also be made clear later.

In operating the circuit on a full duplex basis so that transmission of telegraph messages takes place in both directions at the same time, difficulty may be encountered where interference from the local transmitter T is very heavy', due tothe fact that the signals from the local transmitter T, when transmitted over the line RL at the same time as the desired signals from the distant transmitting station, Wiil tend to overload the repeaters (not shown) in the line RL, and thereby cause distortion of the signals actually received by the telegraph receiving apparatus. Tt therefore becomes necessary to suppress from the line RL the tone frequency corresponding to the tone source G. This is accomplished by swi cliing into the line RL ron the output side of the radio receiver R a suppression lilter RSF, of any well-known type, so designed as to suppress from the line RL the tone frequency corresponding to the source G, while freely passing other frequencies within the voice range. As the inclusion of such a filter in the telephone circuit during tele; phone transmission would tend to suppress from the telephone band frequencies in the neighborhood of the tone from the source G, thereby causing telephonie distort-ion, the arrangement should be such that the suppression iilter RSF is only cut into the circuit when the system is being used for telegraph reception, a pad RP, having an impedance equal to the impedance of the filter in the frequency range outside the band which the latter suppresses, being substituted therefor during telephone reception.

rlhis switching operation is accomplished by selecting some of the energy of the undesired tone from tl e Vlocal transmitter T on the output side of the radio receiver R, and by rectifying the energy, operating a relay train to switch the filter in and'out of the circuit. Accordingly, a circuit` is bridged across the terminals m-g/ which comprises an amplifier RA for amplifying the unwanted tone frequency, a selecting filter RF for selecting such an unwanted tone frequency, and a. detector RD for rectifying the selected current to operate a polar relay PRT The polar relay PRl controls the circuit of a relay PRQ, which in turn opens a circuit of a polar relay PRS. The latter relay controls the switching relays PR.1 and PR5 for switching the filter RSF in and out of circuit. Y

Each of the polar relays PRl, PR2 and FR3 includes an operating winding and a biasing winding, the biasing windings b1, b2 and o3' being connected in series and through a resistance v(which may be 24,00() ohms) to battery. The current iiowing through these biasing windings normally holds theirV armatures against their back contacts, but when a current iiows through Vthe corresponding operating windings of suiiicient strength, a pull is provided upon the armature in the opposite direction, and the armatures of the relays are shifted to their front contacts. When a tone is received the detector RD produces a rectified current through the operating winding 01 which shifts the armature of the relay PR1 to its front or left-hand contact, thereby causing current to iow from ground through the operating winding o2 to battery. The current through the operating` winding of the polar relay PR2 in turn shifts its armature from its right-hand or back contact to its front contact, thereby opening the circuit normally existing from ground through the operating winding 03 of the relay PR3 to battery. The relay PRI.1 thereupon shifts its armature from its front contact to its right-hand or back contact, thereby .completing a circuit from ground, through the operating windings 05 and 0i of the relays PR5 and PR4.r rlhe relays PR.L and PR5 thereupon shift their armatures in such direction as to disconnect the pad RP and substitute therefor the suppression filter RSF. The armature of the relay PR3 at the same time closes the circuit of a signal lamp 30 to indicate that the suppression filter is in circuit.

The relay train above described should be so designed as to prevent false operation due to relatively short telephone and static signals involving frequencies corresponding to the selected tone frequency. Accordingly, the operating and releasing times of the various relays are so set as to take into account the time intervals involved in the transmission of printer signals. Assuming that the printer is operated at a speed of 60 words per minute {aboutQ dots per second) the shortest undistorted marking or tone transmitting impulse due to the printer operation will be about .G22 second. Allowing for a little over twenty-five per cent. distortion, this figure becomes .015 second. The longest spacing or no-tone impulse which would occur will be siX units long, or about .13 second. Under these conditions the relay train should be designed to be unresponsive to impulses or tone groups shorter than about .O15 second. For impulses longer than .015 second the relay PR2 of the train is operated and remains epeated for at least .13 second after the impulse ends, thus providing a hang-over period suflicient to prevent release during the longest no-tone interval which may occur during the transmission of signals. rlhe operation of the relay PR2 in response to an impulse longer than .015 second does not, however', necessarily switch the suppression Vfilter in the circuit as the train should be so designed that this switching operation will not take place in bitrary period such as, say, 1.5 seconds.

lVhen, therefore, a steady tone is received, such as loccurs whenever the local printer is first connected to the circuit, or if interrupted tone is received such as occurs whenever the local printer is connected to the circuit while already sending a message, this Vswitching operation will be performed in 1.5 seconds. In order to insure that a steady tone will be received in the majority of cases, the code is so arranged that the tone is transmitted during the marking interval and not during the spacing` interval. Consequently, the mere fact of connecting the printer to the circuit at the local transmitter results in the transmission of a steady tone until the sen-ding of signals commence, which causes the complete operation of the relay train.

In order that the relay train may have the timing above described, the relays PR.2 and PR3 have associated with their operating windings resistances and condensers for obtainino` slow operation or slow release. In the case of the relay PR2 this relay operates as soon as the 6 M. F. condenser is discharged upon the Vshifting of the armature of PRl to its front contact. A suitable resistance of, say, 3,000 ohms, is included in the discharge circuit so thatv the impulses shorter than .O15 will not cause suiiicient discharge to operate the relay PR2. llVhen the armature of the relay PR2 is shifted to its back Contact, a charging` current flows through the operating winding 02 of the relay PR2 to charge the 6 M. F. condenser, and a resistance of, say, 48,000 ohms, is connected in this charging circuit so'that the charging currentJ will maintain the relay PR2 operated for .13 second after the relay PRI has been released. The relay PR3 is normally operated, and its circuit constants. are such that it will not be released until the relay PR2 has been operated for about 1.5 second. This is due to the charging current for the 20 M. F. condenser which flows through its operating winding 03 and through an 80,000-ohm resistance.l The operating circuit of the relay PR, in response to the release of the relay PRB, is made very quickyacting due to the fact that Vthe charging of the 20 M. F. condenser, which must take place before the winding o3 gets a sufiicient operating current, occurs very quickly in series with the small 50G-ohm resistance. Relays PR4 and PR5 are very V#tast operating and very fast to release, and their operation is controlled by the relay PR3. It will be understood, of course, that the values of the resistances and condensers as above given and as indicated upon the drawings are given only for purposes of illustration, and these values may be widely varied and their proportions with respect to each other may be changed without defeating the result above described. Furthermore, the timing of the relay train as above given is merely illustrative and may be varied through a considerable range depending upon the nature of the telegraph signals transmitted, the speed of transmission and the margin of insurance against false operation deeme necessary in a particular design.

As has been previously stated, the receiving telegraph instrument, such as the receiving printer RP, is operated by the shifting of the armature of the relay PR"1 vin the output circuit of the detector RD', the armature of the relay PR'l sending negative lor positive impulses to the receiving printer RP for marking and spacing signals, respectively. With the code arrangement kpreviously described., in which the tone is trans-V mitted during marking intervalsfand yno tone during the spacing interval, it will be evident that whenever the telegraph senderV at the distant end is disconnected from the jack corresponding to J, the ymarking tone,`

which is normally sent when-no signals are transmitted and which normallyfunctions ing signal to the receiving printer RP, will no longer be received. The result is that the armature of the relay PR"1 will be shifted to its positive contact due to the action of the biasing winding Zi'l and the receiver will then receive a continuous spacing signal so tliatit will continue to operate unless some means is provide to prevent this action. Accordingly, a relay train comprising relays PR"1, PR"2 and PR'3 is provided, the last relay (PR3) ot the train operating to control a relay PR'4 whose armature serves to switch the receiving printer RP from a normal marking battery to a contact which completes the connection from the printer to the armature of the relayl PR'l. This relay train will preferably have the same timing and hang-over features as the relay train previously described Jfor controlling the switching of the suppression tilter RSF. The initial relay PR"1 of the train is a simple polar relay whose winding is infcircuit with the armature of the receiving polar relay PR1, and therefore the armature of the relay PR.'l moves in unison with the armature of the receiving polar re- Y lay; The armature of the polar relay PR"1 controls the circuit of the relay PR'2 in the same way that the relay PR2 of the previous train is controlled by the relay PRl.. In short, the relay PR1 is merely provided be-l cause the usual polar relay oi the type et the relay PRl`r has'only one set ot' contacts. If such relay had two sets of contacts, one of the sets of contacts would be used to control the relay PR'2 and the other relays of the train in exactly the same way as the relay PR1 controls its train.

The result is that when the printer is not connected at the distant sending statiomre'- lays PR' l and PR'2 will kbe released, the lattermaintaining the relayA PR3 operated so that the operating circuit of the switching' relaylPR'4-is'open and the armature ot said relay PR', is held against its left-hand or back contact to connect the receiving printer RP to a negative marking source. rlhis prevents the receiving printer from receiving a continuous positive spacing current over the n armature of the relay PR'l. As soon as the printer is connected to the circuit at the distant sending station, a tone will be received and rectilied by the detector RD'. This tone must continue for a period of, say, .015 sec-v ond in order to enable the relay PR1 to actuate the relay PR', and when the latter relay is actuated, it willnot be released fora period of, say, .13 second, or long enough to los hold over the longest no-tone interval which may occur during the sending vvoit' signals. The relay PR'3, however, will not release in response to the operation of relay PR'Z, une' less the latter relay remains operated con-` tinuouslyfor some'interval such as, for' eX- ample, 1.5.secon`ds- When, however, therelay remains operated for this length of time, as it will when the sending printer isY normally connected to the circuitat the distant station with the consequent transmission of a marking tone or when the printer sender` is actually operating and sending signals, the relay PRS releases, thereby operating the relay PRC, which is quick to operate and quick to release, so that the receiving printer RP is disconnected from the normal marking source and is connected to the armature of the relay P-R1 to receive signals. WhenAthe distant printer is disconnected so that the tone ceases, the relay PR2 releases as soon as the tone has ceased for a period of, say, .13 second, thereby causing the relay PR-3 to operate quickly and through relay PR4 shift the connection of the receiving printer RP to the normal marking source.

In the operation of the system as above described it 'will be noted that the relay train which cuts in the suppression filter RSF at the radio receiver is responsive only to the tone frequency from the local transmitting source G. lnasmuch as theV relay train for cutting in the filter requires about 1.5 seconds for its operation, diiiiculty will be encountered Vif the distant operator should apply her telegraph transmitter to the circuit and start sending before the local operator should plug up her telegraph transmitter TP to the circuit by means of the cord circuit C. Obviously, if the local operator plugs up her telegraph transmitter to theV radio channel after the distant operator has started sending, the tone from the source G will be received and transmittedY over the line RL during the period of a second and a half required for the relay vtrain under the control of the relay PR1 to operate and connect in the suppression lter. This may result in mutilation of the received signal during the period required for the relay train to cut in the suppression filter RSF. The circuit is therefore arranged in accordance withV the present invention so that, when theoperator at one end of the system connects the telegraph transmitter to the radio channel the received tone operates a relay train for automatically vconnecting the transmitting tone to the radio chanel at the other end.-

In order to accomplish this result, a relay S1 is connected to the armature of the polar relay PRl of the telegraph receiving apparatusso that the relay Skwill beY operated whenever the telegraph receiver responds Vto a sending tone applied at the distantstation. The relay Sl which is slow to release has its armature arranged to close the circuit of a slow release relay S2V whenthe armature is retracted. The slow relay S2 in turn, when operated', maintains closed the circuitV of'V a VslowV 'release relay S3.V TheA relay S3 controls ,Y the circuits of av switchingA relay Rl and a lockmg relay .R2 tojautomaticallyconnect the tone from the source G to the radio channel independently of the cord circuit C, in a manner tobe described presently, whenever the telegraph tone is transmitted from the distant transmitter.

The train of relays S1, S2 and S3 which controls the automaticy connection or" the local tone in response to the distant tone, should beso timed as not to Voperate the switching relay R1 in response to voice currents or static signals. As the voice current peaks or static signals will usually be very7 short the relay S1 may be timed to release in about .25 second and the relays S2 and S3 may eachbe arranged to release in about .4l second. The relay S1V being quick to pull up its armature in response to a received tone, it follows that i will require about .8 second for relays lS2 and S3 to successively release and thereby close the circuit of the switching relay R1 so that the relay R1 will not be operated in response to momentary signals such as voice `current peaks and static. The slow release of relay Sl is so timed that when opera-ted said relay will hold up its armature over the interruptions in the received tonerdue to the sending of spacing signals.

The operation of the 'circuit is as follows: Assume that the telegraph transmitters are idle at both endsV of the radio telephone circuit so that no telegraph carrier is bein received from the distant station and the local operator has her plugs P and P removed from the jacks .J and JV. Under these conditions the slow release relay S1 will be de- .energized *As its circuit is connected to the yminal connects her telegraph transmitter to the circuit bythe use of a cord and' plug arrangement similar to the cord circuit C, a tone will be received by the telegraph receiving apparatus RARFRD which causes Vthe polar relay Ptl to shift its armature tothe marking position., thereby connecting negative battery to the circuit of the relay S1 and also to the circuit of the relay- The train of relays controlled by the latter operates as already described to con-l nect the receiving printer RP to the arma ture of the polar relay PRl. In the ineen ltime the relay4 Si" is energized and immediately pullsup its armature to open the circuit of the relay S2 After an interval oi about .fl second the relay S2 releases and in turn opens the circuit ofthe relay S3. The

latter. after 'an additional interval of about 'i cuit over the cord circuit C.

.4 second releases its armature, thereby connecting battery to the windings of the relays R1 and R2. Relay R1 operates and at its armatures connects the source G over the conductors l0 to the two-wire teiniinal of the hybrid coil l0 so that the tone is now transmitted over the transmittingY line TL to the radio transmitter T. This tone upon being received as interference by the local radio receiver R causes the operation of the relay train under the control of the polar relay PRl to connect the suppressionr lter RSF in circuit after an interval of about 1.5 seconds, as already described. The distant operator now transmits signals and these signals will not be mutilated or lost if, while they are being received, thelocal operator uses the cord C to plug from the jack J through the jack J to the transmitting printer TP, because the local transmitting tone is already on the circuit.

It will be noted that when the relay S3 released, the relay R2 was not operated because its circuit is controlled by the springs i of the jack J. Therefore, if the local operator desires to connect up her printer after signaling has started from the distant station, she may insert the plug P in the j ack J and the plug P in the jack J. The circuit of the relay R2 is now completed over the contact of the jack J so that said relay R2 operates and locks up over its right-hand armature independently of the springs of the jack J. At its left armature relay R2 short-circuits the winding of relay R1 which releases, with the result that the tone from the source G no longer is applied to the radio telephone circuit over the conductors l0 but is now applied to the radio telephone cir- The printer or telegraph sender may now be operated in the usual manner without causing any interference with the received telegraph signals.

.ll the operator yno longer has any messages to be transmitted, she may disconnect the local telegraph tone from the radiovtelephone circuit by removingv plugs P and P while the distant telegraph sender is connected to the circuit. Underk these conditions the relay S1 remains operated, relays and S3 remain released, and the relay Rg remains operated since, as already described, it was locked up independently of the contacts of the jack J. The relay R1 was, of course, previously released and con.-` sequently, the local'tone from the source G' will not be applied to the radio telephone circuit unless the operator again plugsup over the cord C. Then the distant telegraph transmitter is disconnected, the relay S1 will be released, Vwhereupon relays S2 land S3 are energized, the latter opening the circuit of the locked up relay R2 which` now releases so that the circuit is restored `to normal. Should the distant operator again Coming again to the condition where both.

telegraph transmitters are connected to the circuit so that the local tone is being transmitted and the distant tone is being received, under these conditions the relay R1 is released and the relay. R2 loclzedkup as alv ready described and the tone from the source G is applied over the cord circuit C. Il?, now, the distant operator should disconnect her transmitter first, relay S.1 will release, so that relays S2' and S3 will be operated and relay R2 will be released (relay R1 having already been released as previously described). The tone from the source G will still be applied to the circuit over the cord circuit C so that the iilter RSF will still be connected in circuit at the radioreceiver R. Under these conditions the local telegraph transmitter may be operated to send signals in the normal manner over the cordcircuit C just as though the relay train S1-S2-S3 were not provided.. L,

It will be understood, oi" course, that the relay trains S1-S2-S'3, together with the Switchingrelay R1 and locking relay R2 and their associated circuits, will also be provided at the distant terminal, so that when either operator comes in on the circuit with the telegraph transmitter the sending tone will be applied to the circuit at the other terminal. f

llVhile theinvention as above outlined is primarily applicable to radio circuits, the principle thereof may be applied to ordinary wire transmission circuits particularly where it is desired to use telegraph printers to pass information relating to calls over toll telephone circuits during idle periods of the circuit.r This application of the principle is-illustrated in Fig. 2 which shows the invention applied to a four-wire telephone circuit, although it will be obvious that it may-be applied to the terminalr two-Way repeater of a two-wire telephone line since the two-way repeater is in effect a short four-wire circuit. y

Referring to Fig. 2, the terminal of a four-wire Vtelephone circuit here shown, the circuit comprising a transmitting line TL and a receiving line RL, including one-way terminal ampliliers TA and RA. respective-l usual terminal jack J. Tone telegraph re ceiving apparatus similar to that described in connection with Fig. l is bridged across the receiving line EL by means of Ya high V 'impedance amplifier RA. The printer apparatus and associated circuits are similar to those described in connection with Fig. l, L

. oper'- o' except that a relay R3 is provided forV switching the receiving printer RP to the contact of the receiving relay PRl. This relay periorins the function of the train ,of relays PRH, PPVZ and Pix/3 of Fig. 1.

Thereis no necessity for a train ot relays in the case of Fig. 2 because no suppression filter corresponding to RSF is connected in to the receiving line in the case of the wire telephone cipuit since the two lines of the four-wire circuit are sufficiently isolated electrically from each other so that undue interference from the transmitting line to the receiving line does not take place.

Further details oi the apparatus will be clear from a description of the operation which is as follows: Y

Assuming that the cord C has been used to connect the four-wire ytelephone circuit to a terminal'telephone line by inserting the plugs P and P in the jacks J and J respectively, speech currents Will pass over the lines ot the tour-Wire circuit in the usual manner.V The high impedance ampli- `ler RA which connects the receivingside of the printer telegraph system to the fourwire circuit does not materially affect the electrical transmission characteristics from a telephone standpoint. A part of the voice currents may tend to pass through the high impedance amplifier, but the narrow band-pass lter RF passes only a narrow band of telephone frequencies to the ampliifier detector RD. The resultant rectiiied pealr currents may intermittently. operate the receiving relay PFtl, but these currents have no eii'ect on the receiving` printer RP- because it is connected in a local circuit which is normally closed by the baclr contact j of the relay R3. This relay is not disturbed by the intermittent operation of the receiving relay PRQ, because of the protection afforded by the release relay'train S1, S2 and S3, thistrain operating in the same manner as the similar train'described in connection with Fig. 1. During the'telephone connection the sending printer TP maintains its circuit-'closed in the idle condition, thus holding the sending relay on its' marlring contact. y c

Let ns now assume that the telephone connection is taken down and that the distant connects sending printerto the at the distant terminal. It Will be circuit understood that the apparatus at the distant tirminal will be identical with that shown in Fig. 2. v The operator at the distant terminal inserts the plugV ycorresponding to P inV tlievjaclr corresponding to J thereat, and inserts the plug lcorresponding to P in the oscillatorcorresponding to G at the distantterminal, through thesending filter correspending'to GF, and over the jacks corresponding to J and J, via the cord corresponding to C, and over the sending side of the four-Wire telephone circuit at Vthe distant terminal. Since the transmitting line at Vthe distant terminal correspor s to the receiving line RL the terminal iiiu ated in Fig. 2, the station shown in Fig 2 will receive this tone over the circuit RL. The tone will now pass through the high inipedance ainplilier RA', and through the filter RF to the amplii'ier detector RD to operate the receiving relay PB1 on its marlring contact. lVlien the receiving relay closes on its marking Contact, the slowrelease relay S1 will be immediately energized, and the slow-release relays S2 and S8 will release in turn alter a short interval. Upon the releasing of relay relays R1 and R3 will be operated. Relay .R3 transfers the receiving printer RP from its local circuit to the armature of the receiving relay PRl. it the same time relay R1 connects the tone from the oscillator to the transmitting line TL by way of the auxiliary circuit l0 and the hybrid. coil l0.

It will be clear. from the operation above described, that the connection of the transmitting printer to the telephone line at the distant terminal results in automatically connecting the transmitting printer TP oit Fig. 2, to the telephone line. The time ot the complete action, from the connection of the printer at the distantstation when the operator puts up the cord, to the automatic connection of the local printer, is determined by the releasing time of the slow-release relays S2 and S3.

The local operator at the station of Fig. 2, may at any time obtain control oi the connection by inserting the plug P of the cord C in the jack J, and byV inserting the plug P of the cord C in the jack J. As a result of this action the auxiliary contacts Vof the jaclr J connect ground'to the relay R2 which was not operated as a result of the automatic action previously described. Since krelay Sais released the relay R2 is now operated, and is locked up independently of the jack J, at its right-hand contact. At its left-hand contact it short-circuits the Winding of the relay R1 thereby disabling the auxiliary circuit l0 so that the tone is nowfapplied to the telephone line over the cord circuit C. The sending printer apparatus may, of course, be disconnected from the line, under' these conditions, at any time, by merely pulling down the cord C.

Y Ii the opeiator at the terminal shown in .Fig 2 rshould initiate the setting up ot a Vprinter connection by connecting jack J to jack J through the cord C thereby con- J will be operated. lll/loinentarily no effect is produced upon the relay Rghowever. At

the distant 'terminalithef teneis applied to the line RL by an automatic yoperation similar to that kalready described 'and as soon as this tone isy received the receiving relay PRl operates the train of relays'Sl', S2' and S3 as before.` Asl soon as relay S3 is released relaysRgvand R3 Will be operated from the left-hand contact of the relay S3.'

With the operation vof the relay R2 the' Wind- .f ot there'l-ay R1 is'at once'short-circnited Whichprevents it from being energized, and consequently the auxiliary circuit 40 does not come intoplay'. Relay lR2 locks up to ground through its ovvn armatureand contact, as before. The local transmitting tone from the source G is transmitted over the ceiver, and means responsive to thesivitch- Iing of the signal transmitter into `connection with vthe radio' transmitter at one ter'- minal to switch Ythe signal transmitter at 2. In ai radio signaling system, a radio transmitter and radio receiver at each terminal, a signal transmitter for each terminal normally disconnected" from the radio receiver, a signal receiver Jfor each terminal normally associated With the corresponding` radio receiver, and means responsive to signals received by the'signal receiver at one terminal from the other terminal to switch the transmitter at said first terminal into connection With the corresponding radio transmitter.

3. In a radio signaling system, a radio transmitter and radio receiver at each terminal, a signal transmitter for each terminal, a link circuit at each terminal whereby an operator may connect the signal transmitter at the terminal to the corresponding radio transmitter, and means responsive to :sucli connections by an operator atene terminal to automatically associatefthe signal transmitter With the radio transmitter at the other station independently of the link uncircuit at the latter terminal.

ec i

4. In a radio signaling system, a radio transmitter and radio receiver at each terminal, a signal transmitter for each terminal, a link circuit at each terminal wherebyY nan operator may connect the signal transy"mitter at the terminal to the corresponding the other terminal into connection with they 3jr corresponding radio transmitter. i

radio transmitter, means responsive to such-r conn'ection by an operator at one terminal to automatically associate the signal transmitter with the radio transmitter at the other station independently of the link circuit at the latter terminal, and means Whereby the operator atsairl latter terminal may establish connection between the signal transmitter and radio transmitter by means of the link circuit While such automatic connection is established. I r

5.V In a radio signaling system, a radio transmitter andradio received at each'terminal, a signal transmitter for eachfterminal, a link circuit at each terminal Where-v.l

by an operator may connect the signal transinitter at the terminal to the corresponding radio transmitter, means responsive to such connection by an operator at one terminaltoautomatically associate the signal transmitter with the radio transmitter atthe other station independently of the link cir-l cuit at the `latter terminal, and' means Whereby the operator at said latter terminal may disconnect the signal transmitter from the* radio transmitter at Will. i 6. AIn a radio signaling system, a radio .transmitter and radio receiver at each terminal, a telegraphtransmitterfor transmitting v signals by an interrupted tone at each terminal, and'means responsive to the connec tionvoi the telegraph transmitter with the radio transmitter at one terminal to applythe tone from the telegraph ltransmitter at the other terminalto the radio transmitter tliereat.

7. In a radio signaling system, a radio transmitter and radio receiver at each terminal, a telegraph transmitter for transmitting'signals by an'interrupted tone at each terminal, a telegraph receiver at 'each termin-al responsive to the toneV transmitted at thevother terminal, and means responsive to the tone received by the telegraph receiver at one terminal fromthe transmitter at the' other terminal to connect the tone from the l telegraph rtransmitterat said lirst terminal tothe corresponding radio transmitter.

"In-a radiosignalingsystem, a radio transmitter and radio receiver at each terminal, a telegraph transmitter tor transmitting signals by an interrupted tone at eachy terminal, a link circuit at each terminal whereby an operator may connect the telegraph transmitter at the terminal to the corresponding radio transmitter, and means other terminal to the radio transmitter thereterminal.

9.Y .In a radio signaling system, a radio transmitter'and radio receiver at each terf minal, a telegraph transmittervfor transmitict ting signals by an interrupted tone ateach terminal, a link circuit at each terminal whereby an operator may connect the telegraph transmitter at the terminal to the corresponding radio transmitter, means responsive to such connection by an operator,l at-k one terminal to automatically apply the tone from the telegraph transmitter at the other terminal to the-radio ltransmitter thereat independently of the link circuit at that terminal, and means whereby the operator at lished.

said latter terminal may establish connection between the signal transmitterl and radio transmitter by means of the link circuit V while .such automatic connection is estab- 10. In a radio signaling system, a radio transmitter and radio receiver `at each ter- 1 miiial, and means whereby the operator at said latter terminal may disconnect the tone from the radioA transmitter at said terminal at will.

1l. In a signaling system, a transmitting jpath anda receiving path at each terminal,

a signal transmitter `for each terminal normally disconnectedl from. the transmitting path, and means responsive to the switching of the signal transmitter into connection l with the transmitting path at one terminal to switch the signal transmitter at the other terminal into connection with the corresponding transmitting path.

12. In a signaling system, a transmitting path and a receiving path at each terminal, a signal transmitter for each terminal normally disconnected fromv the transmitting path, a signal receiver for each terminal normally associated with the corresponding rejceiving path, and means responsive to signals received bythe signal receiver at one terminal from the other terminal to switch the signal transmitter at said first terminal into connection with the corresponding i transmitting path.

`13. In a signaling system, a transmitting path and a receiving path at each terminal, a signal transmitter for each terminal, a link circuit at each terminal whereby an oper- Vator may connect the signal transmitter at the terminal Vfor transmission over the link circuit to the corresponding transmitting path, and means responsive to such'connecter with the transmitting 'path at the other station independently of the link circuit at the latter terminal. i

. 14C. In a signaling'system, a transmitting path and a receivingpathvat each terminal, a signal transmitter for each terminal, a link circuit at each termiiialwhereby an operator may connectA the signal transmitter at the terminal tothe corresponding transmitting path, means responsive to such connection by an operator at one terminal to automatically associate the signal transmitter with the transmitting path at the other station independently-of the link circuit at the latter terminal, and means whereby an operator at said latter terminal may establish connections between the signal transmitter and transmitting path-by means of the link circuit while such automatic connection is established. Y

15.In a signaling system, a transmitting path and a'receiving path at each terminal,

' a signal transmitter for each terminal, a link circuit at each terminal whereby an oper- Vator may connectthe signal transmitter at ator at said latter terminal may disconnect the signal transmitterfrom the transmitting path at will. A i

In testimony whereof, I have signed my name to this specification this 17th day of July,1929.

THOMAS A. McCANN.

tion by an operator at either terminal to 5 automatically associate the signal 'transmit- 

